Ranging Regions for Wireless Communication Relay Stations

ABSTRACT

One embodiment of the present invention provides a unique ranging technique in wireless communication environments that employ relay stations associated with a base station. Each relay station, and optionally the base station itself, can be allocated a unique ranging region having unique ranging resources that may be used by a mobile station to initiate a ranging function with the corresponding relay station or base station.

This application is a 35 USC 371 national phase application ofPCT/IB2007/001452 filed Jun. 1, 2007, which claims priority to U.S.provisional patent application Ser. No. 60/810,573 filed Jun. 2, 2006and U.S. provisional patent application Ser. No. 60/892,510 filed Mar.2, 2007, the disclosures of which are incorporated herein by referencein their entireties.

FIELD OF THE INVENTION

The present invention relates to wireless communications, and inparticular to wireless communication systems that employ relay stations.

BACKGROUND OF THE INVENTION

Wireless communication systems divide areas of coverage into cells, eachof which has traditionally been served by a base station. The basestations support wireless communications with mobile stations. Thecoverage area provided by a given base station is generally referred toas a cell. As the mobile stations move from one cell to another, thecommunication sessions are transferred from one base station to another.Unfortunately, the coverage area for a base station can be limited andmay vary based on geography and structures located within the coveragearea.

In an effort to increase or improve the coverage area provided by basestations, relay stations have been introduced. Relay stations areassociated with a given base station and act as liaisons between themobile stations within the coverage area of the relay stations and thebase station. For downlink communications, data may be transmitted fromthe base station to a relay station and from the relay station to themobile station. For uplink communications, data may be transmitted fromthe mobile station to a relay station and from the relay station to thebase station. As such, the uplink or downlink path may have multiplehops. Further, multiple relay stations may be provided in the uplink ordownlink path. Even when relay stations are employed, mobile stationsand base stations may also communicate directly, if the mobile stationsare within communication range of the base stations.

As the demand for high speed broadband networking over wirelesscommunication networks increases, so too does the demand for differenttypes of networks that can accommodate high speed wireless networking.For example, the deployment of IEEE 802.11-based wireless networks inhomes and business to create Internet access “hot spots” has becomeprevalent in today's society. However, these IEEE 802.11-based wirelessnetworks are relatively limited in bandwidth as well as communicationdistance. Thus, these IEEE 802.11-based wireless networks are not goodcandidates for cellular implementations to provide continuous coverageover extended areas.

In an effort to increase bandwidth and communication distance for longerrange wireless networking, the family of IEEE 802.16 standards wasdeveloped for next generation wireless communications systems that arecellular based. The IEEE 802.16 standards are often referred to asWiMAX, and provide a specification for fixed broadband wirelessmetropolitan access networks (MANs) that use a point-to-multipointarchitecture. Such communications can be implemented, for example, usingorthogonal frequency division multiplexing (OFDM) communication. OFDMcommunication uses a spread spectrum technique to distribute the dataover a large number of carriers that are spaced apart at precisefrequencies.

The IEEE 802.16 standards support high bit rates in both uplink anddownlink communications up to a distance of about 30 miles (˜50 km) tohandle such services as Voice over Internet Protocol (VoIP), IPconnectivity and other voice, media, and data applications. Expecteddata throughput for a typical WiMAX network is 45 MBits/sec. perchannel. IEEE 802.16 networks, such as IEEE 802.16j, networks, can bedeployed as multi-hop networks, which employ relay stations to act asliaisons between base stations and mobile stations and further extendthe effective coverage areas of the associated base stations.

For multi-hop networks, including those employing the IEEE 802.16standards, there is a need for efficient and effective techniques toprovide various ranging functions, channel quality reporting functions,and retransmission control functions when the mobile stations are beingserved by relay stations. These functions are often critical to enablingeffective communications. For example, initial and periodic rangingfunctions help ensure that mobile stations transmit at the appropriatetime and power on the right frequency. The channel quality reportingfunction helps a mobile station identify and select an appropriate basestation or relay station with which to anchor while the retransmissioncontrol function ensures that lost data is retransmitted as necessary.Currently, these functions are controlled primarily by the base stationthat is associated with the relay stations, and the resources of thegroup are often used inefficiently and performance is degraded.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a unique rangingtechnique in wireless communication environments that employ relaystations, which are associated with a base station. Each relay station,and perhaps the base station itself, is allocated a unique rangingregion. Each ranging region has unique ranging resources that may beused by a mobile station to initiate a ranging function with thecorresponding relay station or base station. The mobile station mayselect a relay station for ranging and then select ranging resourcesfrom the ranging region allocated to the selected relay station.

A ranging code is then transmitted by the mobile station using theranging resources for the ranging region allocated to the selected relaystation. The selected relay station will monitor the ranging resourcesassigned to it and detect the ranging code that was transmitted from themobile station. The relay station will take steps to obtain transmissionadjustments for the mobile station in light of receiving the rangingcode, and will send transmission adjustments to the mobile station. Therelay station may send transmission adjustment recommendations with theranging code or information identifying the ranging code to the basestation, which will determine actual transmission adjustments based onthe transmission adjustment recommendations. Alternatively, the relaystation may determine the transmission adjustments without employing thebase station.

The ranging functions may provide initial or periodic ranging functions.Mobile terminals generally use the transmission adjustments from theseranging functions to control the timing, frequency, or power forsubsequent transmissions. An initial ranging function is provided priorto initiating primary communications via the relay station or directlywith the base station. A periodic ranging function is provided duringthe primary communications via the relay station or directly with thebase station.

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a wireless communication environment according to oneembodiment of the present invention.

FIG. 2 illustrates common ranging regions in select frames according toone embodiment of the present invention.

FIG. 3 is communication flow diagram illustrating a common rangingprocess according to one embodiment of the present invention.

FIG. 4 illustrates distributed ranging regions in select framesaccording to one embodiment of the present invention.

FIG. 5 is communication flow diagram illustrating a distributed rangingprocess according to one embodiment of the present invention.

FIG. 6 is communication flow diagram illustrating a periodic rangingprocess according to one embodiment of the present invention.

FIG. 7 is communication flow diagram illustrating an intra-cell fastswitching process employing a synchronized channel quality indicatorchannel according to one embodiment of the present invention.

FIG. 8 is communication flow diagram illustrating an intra-cell fastswitching process employing a non-synchronized channel quality indicatorchannel according to one embodiment of the present invention.

FIG. 9 is a wireless communication environment where a diversitycontroller is provided in the base station according to one embodimentof the present invention.

FIG. 10 is a wireless communication environment where a diversitycontroller is provided in a relay station apart from the relay stationthat is anchoring the mobile station according to one embodiment of thepresent invention.

FIG. 11 is communication flow diagram illustrating macro-diversity fordownlink communications according to one embodiment of the presentinvention.

FIG. 12 is communication flow diagram illustrating macro-diversity foruplink communications according to one embodiment of the presentinvention.

FIG. 13 is a protocol stack according to one embodiment of the presentinvention.

FIGS. 14A and 14B are a communication flow diagram illustrating a firstretransmission control process according to one embodiment of thepresent invention.

FIGS. 15A and 15B are a communication flow diagram illustrating a secondretransmission control process according to one embodiment of thepresent invention.

FIG. 16 is a block representation of a base station according to oneembodiment of the present invention.

FIG. 17 is a block representation of a mobile terminal according to oneembodiment of the present invention.

FIG. 18 is a block representation of a relay station terminal accordingto one embodiment of the present invention.

FIG. 19 is a logical breakdown of an OFDM transmitter architectureaccording to one embodiment of the present invention.

FIG. 20 is a logical breakdown of an OFDM receiver architectureaccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

The present invention provides various techniques for improving wirelesscommunications in wireless communication environments that employ relaystations. In general, relay stations are employed to extend the coveragearea of a given base station by allowing the base station to communicatewith a given mobile terminal via the relay station. With reference toFIG. 1, an exemplary communication environment 10 is illustrated,wherein a basic carrier network 12 supports multiple base stations (BS)14. In general, the base stations 14 are capable of facilitatingwireless communications with any mobile station 16 that is within anavailable communication range. Of the three base stations 14 illustratedin FIG. 1, BS1, BS2, and BS3, base station BS2 is associated withnumerous relay stations 18, RS1-RSN. Given the location of the mobilestation 16, the mobile station 16 may facilitate communications directlywith the base station BS2 or indirectly with the base station BS2through relay stations RS1 and RS2. Notably, the mobile station 16 maybe located in an area that inhibits, and possibly even prohibits, directcommunications with a base station 14, and as such, communications maybe passed through a relay station 18 that is within communication rangeof the mobile station 16.

In most wireless communication environments, extensive efforts are madeto minimize the interference that any given communication session has onother communication sessions within the same area. These efforts tominimize interference generally include controlling when differententities communicate, the channel to use when communicating, and thepower to use to facilitate the communications. Accordingly, the mobilestation 16, base station 14, and relay stations 18 cooperate to ensurethat uplink (UL) communications from different mobile stations 16 arriveat the relay stations 18 or base stations 14 in a synchronized fashionand at relatively the same power levels. Synchronization of thesecommunications generally requires that communications by the mobilestation 16 be synchronized in time, and often in frequency, because thefrequency used for communications defines all or part of the channelused to facilitate the communications.

To facilitate such synchronization, initial ranging techniques areemployed to adjust the timing, frequency, and power that are used by themobile station 16 to facilitate communications. Each mobile station 16will participate in initial ranging prior to initiating communications.Once communications have commenced, periodic ranging may be employed toprovide periodic adjustments to the timing, frequency, and power thatare used by the mobile station 16 to facilitate ongoing communications.For initial or periodic ranging, the mobile station 16 will transmit anappropriate ranging code that is received by a relay station 18 or abase station 14, which will process the ranging code and communicationparameters associated with actually receiving the ranging code todetermine adjustments in timing, frequency, or power for the mobilestation 16 to use for subsequent communications.

A ranging code is transmitted using defined communication resources,which for OFDM may be a defined group of sub-carriers along atime-frequency continuum that defines a transmission frame. Theresources allocated for transmitting ranging codes are generallyreferred to as a ranging region. Each ranging region may includedifferent sets of ranging resources that may be used at the same time bymultiple mobile stations 16, or may be divided and distributed amongmultiple mobile stations 16, such that different mobile stations 16 haveunique ranging resources within a given geographic area.

In one embodiment, a common initial ranging region is provided formultiple mobile stations 16 to use. Accordingly, different mobilestations 16 may use the ranging resources within a common ranging regionat the same time within a given geographic area. Preferably, differentranging code sets are assigned to different ones of the relay stations18 and base stations 14. A ranging code within the code set is selectedby each mobile station 16 and transmitted using the ranging resourceswithin the common ranging region. Thus, the mobile station 16 can alertthe relay stations 18 and the base stations 14 as to its intention ofcommunicating with a particular one of the relay stations 18 or basestations 14 based on the code set from which the ranging code wasselected. FIG. 2 illustrates a scenario where uplink frames intended forrelay stations RS1 and RS2, along with base station BS2, have commonranging regions within which different mobile stations 16 maysimultaneously transmit ranging codes.

With reference to the communication flow diagram of FIG. 3, an exemplarycommon initial ranging process is described. Initially, a mobile station16 will start an initial ranging process (step 100) by selecting aninitial ranging code (IRC) from a code set that is uniquely associatedwith one of the relay stations RS1, RS2, and the base station BS2 (step102). In this case, assume the mobile station 16 is associated withrelay station RS1, but is within communication range of relay stationRS2 and base station BS2. Once the initial ranging code is selected, themobile station 16 will transmit the initial ranging code (step 104).Notably, the initial ranging code transmitted by the mobile station 16may be received by the relay station RS1, the relay station RS2, and thebase station BS2, even through the mobile station 16 intends for the IRCto be received by relay station RS1.

Each of the relay station RS1, relay station RS2, and base station BS2will detect the initial ranging code and determine transmission (TX)adjustment recommendations in light of reception characteristicsassociated with actually receiving and decoding the initial ranging code(steps 106, 108, and 110). The transmission adjustment recommendationsmay relate to any synchronization parameters, such as timing, frequency,and power associated with uplink communications from the mobile station16 to one of the relay station RS1, relay station RS2, and base stationBS2. The relay stations RS1 and RS2 will send code grab messages to thebase station BS2, wherein the code grab messages may include a codeindex corresponding to the initial ranging code that was received, anopportunity index identifying the ranging resources within the commonranging regions that were used for transmitting the initial rangingcode, the mobile station's ID (MSID) if available, and the transmissionadjustment recommendations (steps 112 and 114).

Next, the base station BS2 will process the code grab messages andselect one of the relay stations RS1 and RS2, or itself, to use forsending transmission adjustments back to the mobile station 16 (step116). Selection of one of the relay stations RS1 and RS2 or the basestation BS2 to use for providing the transmission adjustments isgenerally based on the transmission adjustment recommendationsdetermined by the base station BS2 or received from the relay stationsRS1 and RS2. The actual transmission adjustments to provide to themobile station 16 are selected from the transmission adjustmentrecommendations for the selected one of the relay stations RS1 and RS2and the base station BS2. At this point, the base station BS2 will sendtransmission adjustments to the mobile station 16, directly or via theselected relay station RS1 or RS2. In this example, assume the basestation BS2 selected relay station RS2 to provide the transmissionadjustments to the mobile station 16. As such, the base station BS2 willsend a code grab response with transmission adjustments to the relaystation RS2 (step 118), which will send a ranging response with thetransmission adjustments to the mobile station 16 (step 120).

In one embodiment of the present invention, different coordinatedranging regions are provided for associated relay stations 18 and basestations 14. As illustrated in FIG. 4, a different ranging region withinan uplink frame is allocated to relay station RS1, relay station RS2,and base station BS2. As such, different ranging resources are used withdifferent relay stations 18 or base stations 14. Thus, each base station14 and relay station 18 associated with the base station 14 has a uniqueranging region, which may be determined and allocated by the basestation 14. Preferably, the ranging regions of neighboring relaystations 18 and associated base station 14 are orthogonal, in that theresources for the different ranging regions have differenttime-frequency locations within the uplink frame. If the relay stations18 and associated base station 14 are far enough apart whereinterference is not an issue, certain relay stations 18 or base stations14 may have common ranging regions. These ranging regions may be usedfor initial ranging, periodic ranging, bandwidth request ranging, andhandover ranging. Bandwidth request ranging is simply ranging whererequests for more or less bandwidth are being made, whereas handoverranging is ranging in preparation for a handoff from one relay station18 to another, or from a relay station 18 to a base station 14.Accordingly, the ranging region in which a ranging code is transmittedwill indicate the particular relay station 18 or base station 14 towhich transmission of the ranging code was intended. In other words, themobile station 16 can indicate its selection of a particular relaystation 18 or base station 14 based on the ranging region selected fortransmitting the ranging code.

Turning to the communication flow of FIG. 5, a coordinated initialranging process is described according to one embodiment of the presentinvention. Initially, base station BS2, which is associated with relaystations RS1 and RS2, will identify initial ranging regions for each ofthe relay stations RS1 and RS2 (step 200). The different initial rangingregions are assigned to the respective relay stations RS1 and RS2 (steps202 and 204), wherein each relay station RS1 and RS2 is aware of itsunique initial ranging region. Notably, the base station BS2 may alsodetermine a unique initial ranging region for itself.

Assuming the mobile station 16 is aware of the initial ranging regionsassigned to the relay stations RS1 and RS2 and the base station BS2, themobile station 16 will start initial ranging (step 206) by selecting arelay station 18 (or base station 14) based on various downlinkparameters (step 208). The downlink parameters may be varioustransmissions, such as pilot symbol transmissions, from the relaystations RS1 and RS2 and the base station BS2. Assuming the mobilestation 16 selects relay station RS1 for initial ranging, the mobilestation 16 will select a ranging resource from the initial rangingregion of the selected relay station RS1 (step 210). An initial rangingcode is then selected (step 212) and transmitted by the mobile station16 (step 214). Notably, the initial ranging code is sent via the rangingresource of the initial ranging region, which was allocated to relaystation RS1. The initial ranging code transmitted by the mobile station16 will not be processed by relay station RS2 or base station BS2,because the initial ranging code was not transmitted using rangingresources within the initial ranging regions associated with relaystation RS2 or base station BS2. Accordingly, only relay station RS1will detect the initial ranging code and determine transmissionadjustment recommendations that bear on the time, frequency, or powerused to transmit the initial ranging code (step 216).

The relay station RS1 may send to the base station BS2 a code grabmessage identifying a code index associated with the initial rangingcode, an opportunity index identifying the resources used fortransmitting the initial ranging code, the MSID of the mobile station 16if available, and the transmission adjustment recommendations (step218). The base station BS2 will determine transmission adjustments forthe mobile station 16 based on the transmission adjustmentrecommendations (step 220). The base station BS2 will then send a codegrab response including the transmission adjustments to the relaystation RS1 (step 222), which will send the transmission adjustments ina ranging response message to the mobile station 16 (step 224). Althoughthe above example is described in association with initial ranging,handoff, periodic, and bandwidth request ranging may take advantage ofthese techniques.

When mobile stations 16 can communicate with multiple relay stations 18or base stations 14, fast switching and macro diversity handofftechniques may be employed. Fast switching techniques allow a givenmobile station 16 to rapidly switch from one relay station 18 or basestation 14 to another based on channel conditions, resourceavailability, and the like. In general, although the mobile station 16can communicate with multiple ones of the relay stations 18 and basestations 14 at a given time, only one relay station 18 or base station14 is communicated with at any given time. In contrast, macro diversityhandoff, which is often referred to as a soft handoff, allows a mobilestation 16 to simultaneously communicate with two or more relay stations18 and base stations 14 at the same time. Macro diversity handoff maysupport uplink and downlink communications. Accordingly, two or morerelay stations 18 and base stations 14 may receive a transmission from amobile station 16, and may cooperate to either select or combine thereceived information. Similarly, a mobile station 16 may receive thesame information from two or more of the relay stations 18 or basestations 14 and may use selection or combining techniques to recover thetransmitted information. For fast switching or macro diversity handoffs,it is important for the participating relay stations 18 and basestations 14 to have up-to-date ranging information, such that uplink ordownlink communications between the mobile station 16 and one of therelay stations 18 or base stations 14 are properly received andsynchronized with transmissions from other mobile stations 16.

Prior to the present invention, a separate association process wasrequired for each participating relay station 18 and base station 14.During the association process, an initial ranging procedure had to takeplace prior to initiating communications. This association process hasproven to be time-consuming and inefficient. In one embodiment of thepresent invention, a common periodic ranging process is employed toavoid the need for an association process for fast switching and macrodiversity handoff scenarios. In essence, a periodic ranging process isprovided by an anchoring relay station 18 or base station 14. Theanchoring relay station 18 or base station 14 will then share theranging resources with other participating relay stations 18 and basestations 14. Thus, relay stations 18 and base stations 14 that are notanchoring communications with the mobile station 16 have ranginginformation without employing any separate association procedure.

With reference to FIG. 6, an exemplary periodic ranging procedure isprovided according to one embodiment of the present invention. Themobile station 16 will start periodic ranging (step 300) by transmittinga periodic ranging code (PRC) (step 302). Assume that the periodicranging process employs a common periodic ranging region, wherein eachof the relay stations RS1 and RS2 and the base station BS2 share theranging resources within the common periodic ranging region. In thisembodiment, assume that a different periodic ranging code set ofmultiple periodic ranging codes is allocated for each of the relaystations RS1 and RS2 as well as for the base station BS2. Further assumethat relay station RS1 is an anchor for communications with the mobilestation 16, and that the periodic ranging code transmitted by the mobilestation 16 is one that was selected from the periodic ranging code setassigned to the relay station RS1.

Once transmitted, the periodic ranging code is received by relay stationRS1, relay station RS2, and base station BS2, which will detect theperiodic ranging code and the code parameters associated with receivingthe periodic ranging code (steps 304, 306, and 308). In this embodiment,relay station RS1 is able to identify the mobile station 16 thattransmitted the periodic ranging code; however, the relay station RS2and the base station BS2 are not able to identify the mobile station 16that transmitted the periodic ranging code. The relay station RS1 isable to identify the mobile station 16 that transmitted the periodicranging code because the relay station RS1 previously assigned thatparticular code to the mobile station 16, or previously scheduledtransmission of the periodic ranging code by the mobile station 16.Accordingly, the relay station RS1 will identify the mobile station 16that sent the periodic ranging code (step 310) and then determinetransmission adjustments to apply for subsequent communications (step312). The transmission adjustments are sent in a ranging response to themobile station 16 (step 314), which will make the transmissionadjustments and facilitate uplink communications accordingly.

Since the relay station RS2 and the base station BS2 are not able toidentify the mobile station 16 that transmitted the periodic rangingcode, the relay station RS1 will send an update message including a codeindex for the periodic ranging code, an opportunity index identifyingthe resources used to transmit the periodic ranging code, and the MSIDof the mobile station 16 to the base station BS2 (step 316). The basestation BS2 will update its ranging information for the mobile station16 based on information provided by the relay station RS1 (step 318).The base station BS2 will then send a similar update including the codeindex, opportunity index, and MSID that is associated with the periodicranging code received at relay station RS1 to relay station RS2 (step320). Relay station RS2 will update its ranging information for themobile station 16 (step 322). The relay station RS2 and base station BS2will now be able to identify the mobile station 16 that is associatedwith transmitting the periodic ranging codes, and will be betterprepared to participate in fast switching and macro diversity handoffscenarios.

In many fast switching scenarios, the mobile station 16 analyzes channelconditions associated with downlink communications from different relaystations 18 or base stations 14, and determines whether to switch fromone to another based on the channel conditions. Although base stations14 can participate in fast switching with associated relay stations 18,the following discussion focuses on fast switching between two relaystations RS1 and RS2 for clarity and conciseness. In general, a channelquality indication (CQI) is determined by the mobile station 16 andtransmitted over a previously allocated CQI channel. The CQI channel isgenerally allocated to the mobile station 16 by the relay station 18 (orbase station 14) that is currently anchoring communications with themobile station 16. The participating relay stations 18 and base stations14 that are associated with the anchoring relay station 18 (or basestation 14) are called member stations.

In one embodiment, the CQI assignment is synchronized among theparticipating relay stations 18 and base stations 14. The process isbest illustrated in association with the communication flow of FIG. 7.Initially, assume an anchoring relay station RS1 selects a CQI channelfor use by the mobile station 16 (step 400) and transmits a CQI channelallocation identifying the selected CQI channel to the mobile station 16(step 402). To synchronize the CQI channel assignment, the anchoringrelay station RS1 will send a CQI channel update identifying the CQIchannel allocated for the mobile station 16 and the MSID of the mobilestation 16 to the base station 14 (step 404). The base station BS2 willsend a similar CQI channel update to the relay station RS2 (step 406).The relay station RS2 will make note of the CQI channel being used bythe mobile station 16 and provide a CQI channel update response toconfirm receipt of the CQI channel information to the base station BS2(step 408). The base station BS2 will also send a CQI channel updateresponse to the anchoring relay station RS1 to indicate that the CQIchannel information has been provided to the relay station RS2 (step410).

During this time, the mobile station 16 will monitor the channel qualityof the link between the mobile station 16 and the anchoring relaystation RS1, and will transmit a corresponding channel quality indicatorvia the allocated CQI channel (step 412). The channel quality indicatormay be received and monitored by the anchoring relay station RS1 as wellas the relay station RS2. The mobile station 16 will also monitor thechannel quality associated with the relay station RS2. The mobilestation 16 will monitor the channel quality of the links with the anchorrelay station RS1 and the relay station RS2, and at some point, thechannel quality associated with the link with relay station RS2 willbecome better than that of the link associated with the anchor relaystation RS1. At this point, the mobile station 16 may decide to switchcommunications from the anchor relay station RS1 to the relay stationRS2 (step 414). Accordingly, the mobile station 16 will send a switchingrequest via the allocated CQI channel to indicate the desire to switchcommunications from the anchoring relay station RS1 to relay station RS2(step 416). The switching request may be received by the anchoring relaystation RS1 and relay station RS2, and in response, the anchoring relaystation RS1 and relay station RS2 will send switching alert messagesindicating the desire of the mobile station 16 to switch from theanchoring relay station RS1 to relay station RS2 (steps 418 and 420).Notably, the switching alert message will identify at least the relaystation RS2 to which communications are to be switched, and the MSID ofthe mobile station 16.

The base station BS2 may determine whether to prevent the mobile station16 from switching communications from the anchoring relay station RS1 torelay station RS2 (step 422). If the base station BS2 does not interveneto prevent switching, the anchoring relay station RS1 will send aswitching response to indicate that switching from the anchoring relaystation RS1 to relay station RS2 is authorized (step 424). At thispoint, the mobile station 16 and the relay station RS2 begin supportingcommunications, and thus the relay station RS2 becomes the anchoringrelay station (step 426).

Once communications are established with relay station RS2, relaystation RS2 may send a message indicating that the switch has beencompleted to the base station BS2 (step 428). With this embodiment, thetargeted (relay or base) station to which communications are beingswitched is notified of the desire to switch by the mobile station 16 asthe currently anchoring (relay or base) station.

With reference to FIG. 8, a communication flow is illustrated whereinthe CQI channel is not synchronized. Initially, an anchoring relaystation RS1 selects a CQI channel for use by the mobile station 16 (step500). The CQI channel is assigned to the mobile station 16 via a CQIchannel allocation message (step 502), wherein the mobile station 16will provide channel quality indicators via the CQI channel to theanchoring relay station RS1 (step 504). As above, the mobile station 16will monitor channel quality associated with links with the anchoringrelay station RS1 and the relay station RS2, and at some point willdecide to switch communications from the anchoring relay station RS1 torelay station RS2 (step 506). The mobile station 16 will send aswitching request via the CQI channel to the anchoring relay station RS1(step 508). The anchoring relay station RS1 will send a switchingrequest alert identifying the targeted relay station RS2 and the mobilestation 16 to the base station BS2 (step 510). The base station BS2 willsend a switching alert to the targeted relay station RS2 and identifythe mobile station 16 using the MSID for the mobile station 16 (step512). The targeted relay station RS2 will select a CQI channel for themobile station 16 to use when reporting channel quality to the targetedrelay station RS2 (step 514). The relay station RS2 will then send aswitching alert response back to the base station BS2, wherein theswitching alert response including the selected CQI channel and the MSIDfor the mobile station 16 (step 516). In response, the base station BS2will send a switching alert response message to the currently anchoringrelay station RS1 (step 518). Again, the switching alert responsemessage will include the CQI channel for the mobile station 16 to usefor providing CQI to the targeted relay station RS2. The anchoring relaystation RS1 will send a switching request response including the new CQIchannel to the mobile station 16 (step 520). At this point, the mobilestation 16 will provide a CQI for the channel quality associated withthe link with relay station RS2 via the new CQI channel (step 522).During this time, the mobile station 16 will switch communications fromthe relay station RS1 to the relay station RS2, which is not theanchoring relay station for communications (step 524). The relay stationRS2 may send a switch complete message to the base station BS2 toindicate that communications have been switched from relay station RS1to relay station RS2 (step 526). From the above, CQI channel allocationmay be employed to enhance fast switching techniques among associatedrelay stations 18 and base stations 14.

Macro diversity may take on various configurations depending on thelocation of the relay stations 18 relative to the associated basestation 14 and the mobile station 16 being served. With reference toFIG. 9, uplink or downlink macro diversity may be provided between relaystation RS1 and relay station RS2, as well as with base station 14.Uplink or downlink communications associated with the relay station RS1are relayed between the relay station RS1 and the base station 14.Similarly, communications between relay station RS2 and the mobilestation 16 are relayed between the relay station RS2 and the basestation 14. As noted, uplink and downlink communications may besupported directly by the base station 14 as well. For downlinkcommunications, the base station 14 will send the same data to betransmitted to the mobile station 16 to the relay station RS1 and therelay station RS2, and at a certain time on a given channel, the relaystation RS1, relay station RS2, and base station 14 may transmit thesame information to the mobile station 16, which will receive thedownlink transmission and combine them to recover the transmittedinformation. The relay or base stations 18, 14 participating in macrodiversity for a given mobile station 16 define a macro diversity set.Generally, the anchoring station, which is illustrated as being relaystation RS1, will provide a diversity control function. With the presentinvention, the diversity control function is provided in a diversitycontroller (DC) 19, which need not be in the relay or base station 18,14 that is the anchor station. As illustrated in FIG. 9, the diversitycontroller 19 is provided in the base station 14, even though relaystation RS1 acts as an anchor station for the mobile station 16. Thus,the primary link for communications is between relay station RS1 and themobile station 16; however, the mobile station 16 may combinetransmissions from the relay station RS1, the relay station RS2, and thebase station 14. Similarly, transmissions from the mobile station 16 maybe received by the relay station RS1 and relay station RS2, andforwarded to the base station 14, wherein the base station 14 willcombine the transmissions received via the relay stations RS1 and RS2 aswell as those received directly at the base station 14 to recover thetransmitted information. Notably, the initial and periodic rangingtechniques described above can be used to identify the participatingrelay stations 18 and base stations 14, in a macro diversity (orhandoff) set.

Preferably, the diversity controller 19 is provided in the base station14 for the macro diversity set, or the relay station 18 that is closestto the base station 14 in the macro diversity set, as illustrated inFIGS. 9 and 10, respectively. In FIG. 10, the relay station RS2 canactually transmit information intended for the mobile station 16 viarelay station RS1, which as illustrated, acts as an anchor station forthe mobile station 16. For uplink macro diversity, transmissions fromthe mobile station 16 are received by relay station RS1 and relaystation RS2. Relay station RS1 will forward the received information torelay station RS2, which will combine the information to recover thetransmitted information, and then provide the transmitted information tothe base station 14. For downlink communications, the diversitycontroller 19 of the relay station RS2 may send information to betransmitted to the mobile station 16 to the relay station RS1, and at adefined time and over an appropriate channel, both the relay station RS2and the relay station RS1 will transmit information to the mobilestation 16. Thus, the diversity controller 19 is responsible formulticasting downlink communications to any downstream relay stations 18and to the mobile station 16, as well as combining direct transmissionsfor uplink communications. Again, the diversity controller 19 ispreferably provided in the base station 14 itself or in the relaystation 18 that is closest to the base station 14 of the macro diversityset, regardless of the anchoring relay or base station. Further, therelay station 18 or base station 14 that provides the diversitycontroller 19 may control the scheduling of uplink and downlinkcommunications for the mobile station 16. As the mobile station 16moves, the diversity controller 19 allocated to the mobile station 16may move from station to station.

The base station 14 may always provide the diversity controller 19.However, if the diversity controller 19 is not in the base station 14,the diversity controller 19 may be provided in the anchor relay station18, which may be employed to schedule uplink and downlink transmissions.Alternately, the anchor relay station 18 may schedule transmissions andthen inform the diversity controller 19, which may be located in thesame or in a different relay station 18. In general, the anchor stationis the station from which the mobile station 16 receives the strongestdownlink signal.

With reference to FIG. 11, a communication flow is provided toillustrated downlink communications in a macro diversity scenario forthe communication environment of FIG. 9. Initially, assume the diversitycontroller 19 is located in the base station 14, and relay station RS1is an anchor station for the mobile station 16. The diversity controller19 of the base station 14 will multicast data intended for the mobilestation 16 to the relay stations RS1 and RS2 (step 600). The multicastmay also include information identifying a resource allocation for thedownlink communications, and as such, the relay stations RS1 and RS2will be informed of the resources to use when transmitting the data tothe mobile station 16. The diversity controller 19 of the base station14 may also send a downlink (DL) map, which identifies the downlinkresources that will be used for transmissions to the mobile station 16by the relay stations RS1 and RS2, and perhaps the base station 14 (step602). At the appropriate time and using the appropriate channel in lightof any transmission adjustments from prior ranging operations, relaystation RS1, relay station RS2, and the base station 14 may transmit thesame data to the mobile station 16 (steps 604A, 604B, and 604C). themobile station 16 will receive these transmissions at substantially thesame time and combine the transmissions from relay station RS1, relaystation RS2, and the base station 14 to recover the transmittedinformation (step 606).

With reference to FIG. 12, an uplink communication scenario isillustrated for the macro diversity of FIG. 9. Again, the diversitycontroller 19 is provided in the base station 14, and relay station RS1is an anchor station for the mobile station 16. Initially, the basestation 14 will provide uplink resource allocations for thetransmissions for the mobile station 16 to the relay stations RS1 andRS2 (step 700). The base station 14 will also send an uplink (UL) mapmessage identifying the uplink resources that will be used by relaystations RS1 and RS2, and perhaps the base station 14 to the mobilestation 16 (step 702). The mobile station 16 will then transmit data atthe allocated time and over the allocated channel (step 704). Thetransmitted data may be received by the relay station RS1, relay stationRS2, and the base station 14. Accordingly, the relay station RS1 willforward the data received from the mobile station 16 to the base station14 (step 706A). The relay station RS2 will send the data it receivedfrom the mobile station 16 to the base station 14 (step 706B). At thispoint, the base station 14 will combine the data from the transmissionsreceived from relay stations RS1 and RS2, as well as directly at thebase station 14 to recover the information transmitted by the mobilestation 16 (step 708).

Another embodiment of the present invention relates to implementation ofan improved error control technique. In particular, an automatic repeatrequest (ARQ) mechanism and a hybrid ARQ mechanism cooperate to provideefficient retransmission of data. In general, ARQ is an error controlmethod for data transmission systems, and employs acknowledgementmessages and timeout mechanisms to ensure that all data that istransmitted is properly received. Typically, an acknowledgement messageis sent by a receiver to the transmitter to indicate that each datapacket is correctly received. Generally, when the transmitter does notreceive an acknowledgement before a timeout occurs, the transmitter willretransmit the frame. The receiver may send a negative acknowledgementif it is determined that a packet is not properly received, or is lost.Hybrid ARQ is a variant of ARQ, and generally employs some type ofcoding within each data packet to indicate whether or not the datapackets were properly received. For example, each packet may be encodedwith an error correction code. As the packets are received, they areanalyzed in light of the error correction code to determine whether ornot each of the packets was received. If a packet must be retransmitted,the receiver may request retransmission of the packet.

In a communication environment employing relay stations 18, multiplehops are required to reach a mobile station 16 from a base station 14.Generally, the hops from a base station 14 to a relay station 18 andbetween relay stations 18 are relatively reliable. The least reliablehop is between the last relay station 18 in the path and the mobilestation 16. In many instances, the probability of a failed transmissionattempt is very high in this last hop due to the changing channelconditions associated with the mobility of the mobile station 16. Whenemploying basic ARQ techniques when relay stations 18 are employed, thebase station 14 must re-send data through the relay stations 18 to themobile station 16, even though the only failed link is between the lastrelay station 18 and the mobile station 16. Thus, significant resourcesare wasted by retransmitting the packets from the base station 14 to thelast relay station 18 in the forwarding path.

For the present invention, ARQ is employed at a MAC, or layer 2, level,while hybrid ARQ is employed at a physical, or layer 1, level. Further,ARQ is performed on an end-to-end basis across multiple links betweenentities, wherein hybrid ARQ is performed on a per-link basis. Withreference to FIG. 13, an exemplary protocol stack is illustrated inwhich the cooperation of ARQ and hybrid ARQ is provided. The physicallayer (layer 1) employs hybrid ARQ for retransmission control on aper-link basis. As such, an individual hybrid ARQ retransmission processis provided between the base station 14 and the relay station RS2;between the relay station RS2 and the relay station RS1; and between therelay station RS1 and the mobile station 16. Above the physical layerresides a MAC layer in which ARQ retransmission control is provided.Notably, ARQ retransmission techniques may be provided between the basestation 14 and the mobile station 16 at the MAC layer. Within the MAClayer, an R-MAC layer is provided for the base station 14, relay stationRS2, and relay station RS1. The relay station RS1 may also employ aMAC-lite layer to facilitate an ARQ process with the mobile station 16.The R-MAC layers of the base station 14, relay station RS2, and relaystation RS1 may be employed to provide ARQ processes between the basestation 14 and the relay station RS2, as well as between relay stationRS2 and relay station RS1, depending on the configuration of theembodiment.

In one embodiment, the last relay station 18, which is the onecommunicating directly with the mobile station 16, will keep track ofthe service data unit sequence numbers (SDU_SN) associated with eachpacket data unit (PDU) or PDU_SN, or the like, that is received. Whenthe mobile station 16 realizes that a PDU is lost or corrupted, themobile station 16 will send a negative acknowledgement message to thebase station 14. After the base station 14 receives the ARQ or thenegative acknowledgement, the base station 14 may send a retransmissionrequest identifying the SDU_SNs associated with the PDUs to beretransmitted to the last relay station 18, and perhaps schedulinginformation for retransmitting the PDUs. The last relay station 18 willsend a retransmission response indicating whether or not the PDUs to beretransmitted are still available at the last relay station 18. If thePDUs are available at the last relay station 18, the last relay station18 will retransmit those PDUs to the mobile station 16. Otherwise, thebase station 14 will retransmit the PDUs to be retransmitted directly orindirectly to the last relay station 18, which will then retransmit thePDUs to the mobile station 16. The messages exchanged between the basestation 14 and the last relay station 18 may identify the communicationor call using a communication ID (CID) as well as the SDU_SNs for thePDUs that need to be retransmitted. Further, the last relay station 18may identify the SDU_SNs for both the available and the unavailable PDUsat the last relay station 18.

With reference to FIGS. 14A and 14B, an exemplary communication flow isprovided to illustrate cooperation of ARQ and hybrid ARQ according toone embodiment. Initially, assume PDU P1 is transmitted from the basestation 14 to relay station RS2 in an effort to deliver the PDU P1 tothe mobile station 16 (step 800). Assume that the relay station RS2 didnot receive the PDU P1, and using a hybrid ARQ retransmission technique,determined that the PDU P1 was lost or not properly detected, asindicated by the X. In response, the relay station RS2 will send ahybrid negative acknowledgement message (H-NACK) back to the basestation 14 via the physical layer (step 802). In response, the basestation 14 will retransmit PDU P1 (step 804). Assuming that the relaystation RS2 properly received PDU P1, a hybrid acknowledgement message(H-ACK) is transmitted to the base station 14 via the physical layer(step 806). Assuming that relay station RS1 is the last relay station inthe downlink path, relay station RS2 will forward the PDU P1 to therelay station RS1 (step 808). If RS1 properly receives the PDU P1, anH-ACK is sent back to relay station RS2 at the physical layer (step810).

At this point, the relay station RS1 has received PDU P1, and willattempt to transmit the PDU P1 to the mobile station 16 (step 812).Assume that the PDU P1 was not properly received. The mobile station 16is able to determine that the PDU P1 was not properly received, andsends an H-NACK back to the relay station RS1 via the physical layer toindicate that the PDU P1 was not properly received (step 814). The relaystation RS1 may attempt to retransmit the PDU P1 automatically inresponse to receiving the H-NACK (step 816). Further assume that the PDUP1 is not received during retransmission, and as such the mobile station16 provides another H-NACK back to the relay station RS1 via thephysical layer (step 818).

During this time, assume that the base station 14 attempts to send asecond PDU P2 to relay station RS2 for ultimate delivery to the mobilestation 16 (step 820). If the PDU P2 is properly received, the relaystation RS2 will send an H-ACK back to the base station 14 via thephysical layer (step 822). The relay station RS2 will then forward thePDU P2 to the relay station RS1 (step 824), wherein if the PDU P2 isproperly received, an H-ACK is sent back to the relay station RS2 viathe physical layer (step 826). Next, the relay station RS1 will attemptto transmit the PDU P2 to the mobile station 16 (step 828). Assumingthat the PDU P2 is properly received by the mobile station 16, an H-ACKis sent back to the relay station RS1 via the physical layer (step 830).

At this point, the mobile station 16 may look at the SDU_SN of the PDUP2 and recognize that PDU P1 was not received. As such, the mobilestation 16 may send a negative acknowledgement message (NACK) indicatingthat PDU P1 was not received via the MAC layer (step 832). The NACK mayinclude the sequence numbers for the PDUs that were not received,including PDU P1. The base station 14 will respond by sending aretransmission request to the relay station RS1 directly or via relaystation RS2 (step 834). The retransmission request will include thecommunication IDs as well as the sequence numbers for the PDUs to beretransmitted. The relay station RS1 will acknowledge receipt of theretransmission request and identify the sequence numbers for the PDUs ithas available for retransmission in a retransmission response, which issent back to the base station 14 (step 836).

At this point, the relay station RS1 will attempt to retransmit the PDUP1, which has been stored since its receipt from the relay station RS2(at step 808) to the mobile station 16 (step 838). If the PDU P1 is notproperly received, the mobile station 16 may detect this and send anH-NACK back to the relay station RS1 via the physical layer (step 840).The relay station RS1 may attempt to retransmit the PDU P1 (step 842).Upon proper receipt, the mobile station 16 may send an H-ACK back to therelay station RS1 (step 844).

In yet another embodiment, the last relay station 18 may identify a lostPDU in response to receiving an H-NACK from the mobile station 16. Inresponse, the last relay station 18 may send a retransmission reportthat identifies the lost PDUs to the base station 14. In response, thebase station 14 may send a retransmission request to the last relaystation 18, which will retransmit the lost PDUs. Notably, the basestation 14 may ignore any subsequent ACK or NACK messages that areprovided at the MAC layer. In this embodiment, authorization toretransmit lost PDUs is quickly provided to the last relay station 18.An overview of this embodiment is provided in the communication flow ofFIGS. 15A and 15B.

Initially, assume PDU P1 is transmitted from the base station 14 torelay station RS2 in an effort to deliver the PDU P1 to the mobilestation 16 (step 900). Assume that the relay station RS2 did not receivethe PDU P1, and using a hybrid ARQ retransmission technique, determinedthat the PDU P1 was lost or not properly detected, as indicated by theX. In response, the relay station RS2 will send a hybrid negativeacknowledgement message (H-NACK) back to the base station 14 via thephysical layer (step 902). In response, the base station 14 willretransmit PDU P1 (step 904). Assuming that the relay station RS2properly received PDU P1, a hybrid acknowledgement message (H-ACK) istransmitted to the base station 14 via the physical layer (step 906).Assuming that relay station RS1 is the last relay station in thedownlink path, relay station RS2 will forward the PDU P1 to the relaystation RS1 (step 908). If RS1 properly receives the PDU P1, an H-ACK issent back to relay station RS2 at the physical layer (step 910).

At this point, the relay station RS1 has received PDU P1, and willattempt to transmit the PDU P1 to the mobile station 16 (step 912).Assume that the PDU P1 was not properly received. The mobile station 16is able to determine that the PDU P1 was not properly received, andsends a H-NACK back to the relay station RS1 via the physical layer toindicate that the PDU P1 was not properly received (step 914). The relaystation RS1 may attempt to retransmit the PDU P1 automatically inresponse to receiving the H-NACK (step 916). Further assume that the PDUP1 is not received during retransmission, and as such the mobile station16 provides another H-NACK back to the relay station RS1 via thephysical layer (step 918).

At this point, the relay station RS1, through the H-NACK, will recognizethat PDU P1 was not properly received by the mobile station 16. Inresponse, the relay station RS1 will send a retransmission reportdirectly or indirectly to the base station 14 (step 920). Theretransmission report may identify PDU P1 directly or through a sequencenumber and the associated communication ID. The base station 14 mayprocess the retransmission report and send a retransmission request toinstruct the relay station RS1 to retransmit PDU P1 to the mobilestation 16 (step 922). The retransmission request may identify thesequence numbers for the PDUs to be retransmitted along with thecommunication IDs. Notably, these messages may identify PDUs for thesame or different communication IDs, and may include one or moresequence numbers for any number of PDUs. The relay station RS1 mayrespond by sending a retransmission response back to the base station 14indicating that the retransmission request was received, and confirmingthe PDUs to be retransmitted for the corresponding communication IDs(step 924).

During this time, assume that the base station 14 attempts to send asecond PDU P2 to relay station RS2 for ultimate delivery to the mobilestation 16 (step 926). If the PDU P2 is properly received, the relaystation RS2 will send an H-ACK back to the base station 14 via thephysical layer (step 928). The relay station RS2 will then forward thePDU P2 to the relay station RS1 (step 930), wherein if the PDU P2 isproperly received, an H-ACK is sent back to the relay station RS2 viathe physical layer (step 932). Next, the relay station RS1 will attemptto transmit the PDU P2 to the mobile station 16 (step 934). Assumingthat the PDU P2 is properly received by the mobile station 16, an H-ACKis sent back to the relay station RS1 via the physical layer (step 936).

At this point, the mobile station 16 may look at the SDU_SN of the PDUP2 and recognize that PDU P1 was not received. As such, the mobilestation 16 may send a negative acknowledgement message (NACK) indicatingthat PDU P1 was not received via the MAC layer (step 938). Since thebase station 14 has already recognized that PDU P1 was not properlyreceived and has already sent a request instructing relay station RS1 toretransmit PDU P1 to the mobile station 16, the NACK that was receivedvia the MAC layer may be ignored.

In response to the retransmission request, the relay station RS1 willthen attempt to retransmit the PDU P1 to the mobile station 16 (step940). If the PDU P1 is not properly received, the mobile station 16 maydetect this and send an H-NACK back to the relay station RS1 via thephysical layer (step 942). The relay station RS1 may attempt toretransmit the PDU P1 (step 944). Upon proper receipt, the mobilestation 16 may send an H-ACK back to the relay station RS1 (step 946).

A high level overview of the mobile stations 16 and base stations 14 ofthe present invention is provided in following discussion. Withreference to FIG. 16, a base station 14 configured according to oneembodiment of the present invention is illustrated. The base station 14generally includes a control system 20, a baseband processor 22,transmit circuitry 24, receive circuitry 26, one or more antennas 28,and a network interface 30. The receive circuitry 26 receives radiofrequency signals bearing information from one or more remotetransmitters provided by mobile stations 16 or relay stations 18.Preferably, a low noise amplifier and a filter (not shown) cooperate toamplify and remove broadband interference from the signal forprocessing. Downconversion and digitization circuitry (not shown) willthen downconvert the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (DSPs). Thereceived information is then sent across a wireless network via thenetwork interface 30 or transmitted to another mobile station 16 orrelay station 18 serviced by the base station 14. The network interface30 will typically interact with a base station controller and acircuit-switched network forming a part of the access network, which maybe coupled to the public switched telephone network (PSTN) to form thecarrier network 12.

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of control system 20, whichencodes the data for transmission. The encoded data is output to thetransmit circuitry 24, where it is modulated by a carrier signal havinga desired transmit frequency or frequencies. A power amplifier (notshown) will amplify the modulated carrier signal to a level appropriatefor transmission, and deliver the modulated carrier signal to theantennas 28 through a matching network (not shown). Modulation andprocessing details are described in greater detail below.

In order to allow the relay station 18 or mobile station 16 to requestbandwidth or additional bandwidth, quality of service information mustbe provided along with the request. Quality of service information mayinclude priority, service class, scheduling information, or the like.

With reference to FIG. 17, a mobile station 16 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 14, the mobile station 16 will include a control system 32,a baseband processor 34, transmit circuitry 36, receive circuitry 38,one or more antennas 40, and user interface circuitry 42. The receivecircuitry 38 receives radio frequency signals bearing information fromone or more base stations 14 or relay stations 18. Preferably, a lownoise amplifier and a filter (not shown) cooperate to amplify and removebroadband interference from the signal for processing. Downconversionand digitization circuitry (not shown) will then downconvert thefiltered, received signal to an intermediate or baseband frequencysignal, which is then digitized into one or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations, as will be discussed on greater detail below. Thebaseband processor 34 is generally implemented in one or more digitalsignal processors (DSPs) and application specific integrated circuits(ASICs).

For transmission, the baseband processor 34 receives digitized data,which may represent voice, data, or control information, from thecontrol system 32, which it encodes for transmission. The encoded datais output to the transmit circuitry 36, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antennas 40 through a matching network(not shown). Various modulation and processing techniques available tothose skilled in the art are applicable to the present invention.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation generally employs an Inverse Fast Fourier Transform(IFFT) on the information to be transmitted. For demodulation, theperformance of a Fast Fourier Transform (FFT) on the received signal isrequired to recover the transmitted information. In practice, theInverse Discrete Fourier Transform (IDFT) and Discrete Fourier Transform(DFT) are implemented using digital signal processing for modulation anddemodulation, respectively.

Accordingly, the characterizing feature of OFDM modulation is thatorthogonal carrier waves are generated for multiple bands within atransmission channel. The modulated signals are digital signals having arelatively low transmission rate and capable of staying within theirrespective bands. The individual carrier waves are not modulateddirectly by the digital signals. Instead, all carrier waves aremodulated at once by IFFT processing.

In the preferred embodiment, OFDM is used at least for the downlinktransmission from the base stations 14 or relay stations 18 to themobile stations 16. Further, the base stations 14 are synchronized to acommon clock via GPS signaling and coordinate communications via a basestation controller. Each base station 14 may be equipped with n transmitantennas 28, and each mobile station 16 is equipped with m receiveantennas 40. Notably, the respective antennas can be used for receptionand transmission using appropriate duplexers or switches and are solabeled only for clarity. Notably, the present invention is equallyapplication to single antenna embodiments at the mobile station 16,relay stations 18, and the base stations 14.

With reference to FIG. 18, a relay station 18 configured according toone embodiment of the present invention is illustrated. Notably, thebasic architecture of a relay station 18 is very analogous to a mobilestation 16 with the exception that the relay station 18 is able tocommunicate wirelessly with base stations 14 as well as mobile stations16. Accordingly, the relay station 18 will include a control system 32′,a baseband processor 34′, transmit circuitry 36′, receive circuitry 38′,one or more antennas 40′, and user interface circuitry 42′. The receivecircuitry 38′ receives radio frequency signals bearing information fromone or more base stations 14 or mobile stations 18 and the transmitcircuitry 36′ transmits radio frequency signals to one or more basestations or mobile stations. The baseband processor 34′ and controlsystem 32′ operate in a fashion similar to the corresponding elements ofthe mobile station 16 and the base station 14.

With reference to FIG. 19, a logical OFDM transmission architecture of amobile station 16, base station 14, or relay station 18 is providedaccording to one embodiment. For clarity and conciseness, assume thefollowing transmission architecture is in a base station 14. The data 44to be transmitted is a stream of bits, which is scrambled in a mannerreducing the peak-to-average power ratio associated with the data usingdata scrambling logic 46. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC logic 48. Next, channel coding is performed using channel encoderlogic 50 to effectively add redundancy to the data to facilitaterecovery and error correction at the mobile station 16. The channelencoder logic 50 uses known Turbo encoding techniques in one embodiment.The encoded data is then processed by rate matching logic 52 tocompensate for the data expansion associated with encoding.

Bit interleaver logic 54 systematically reorders the bits in the encodeddata to minimize the loss of consecutive data bits. The resultant databits are systematically mapped into corresponding symbols depending onthe chosen baseband modulation by mapping logic 56. Preferably,Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key(QPSK) modulation is used. The symbols may be systematically reorderedto further bolster the immunity of the transmitted signal to periodicdata loss caused by frequency selective fading using symbol interleaverlogic 58.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. Blocks of symbols arethen processed by space-time block code (STC) encoder logic 60, whichmodifies the symbols in a fashion making the transmitted signals moreresistant to interference and more readily decoded at a mobile station16. The STC encoder logic 60 will process the incoming symbols andprovide n outputs corresponding to the number of transmit antennas 28for the base station 14. The control system 20 and/or baseband processor22 will provide a mapping control signal to control STC encoding. Atthis point, assume the symbols for the n outputs are representative ofthe data to be transmitted and capable of being recovered by the mobilestation 16. See A. F. Naguib, N. Seshadri, and A. R. Calderbank,“Applications of space-time codes and interference suppression for highcapacity and high data rate wireless systems,” Thirty-Second AsilomarConference on Signals, Systems & Computers, Volume 2, pp. 1803-1810,1998, which is incorporated herein by reference in its entirety.

For the present example, assume the base station 14 has two antennas 28(n=2) and the STC encoder logic 60 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 60 is sent to a corresponding IFFT processor 62,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing alone or in combination with otherprocessing described herein. The IFFT processors 62 will preferablyoperate on the respective symbols using IDFT or like processing toeffect an inverse Fourier Transform. The output of the IFFT processors62 provides symbols in the time domain. The time domain symbols aregrouped into frames, which are associated with prefix and pilot headersby like insertion logic 64. Each of the resultant signals isup-converted in the digital domain to an intermediate frequency andconverted to an analog signal via the corresponding digitalup-conversion (DUC) and digital-to-analog (D/A) conversion circuitry 66.The resultant (analog) signals are then simultaneously modulated at thedesired RF frequency, amplified, and transmitted to via the RF circuitry68 and antennas 28. Notably, the transmitted data is preceded by pilotsignals, which are known by the intended mobile station 16 andimplemented by modulating the pilot header and scattered pilotsub-carriers. The mobile station 16 may use the scattered pilot signalsfor channel estimation and interference suppression and the header foridentification of the base station 14. Again, this architecture may beprovided in relay stations 18 and mobile stations 16.

Reference is now made to FIG. 20 to illustrate reception of thetransmitted signals by a mobile station 16; however, the principles maybe applied to a base station 14 or relay station 18 Upon arrival of thetransmitted signals at each of the antennas 40 of the mobile station 16,the respective signals are demodulated and amplified by corresponding RFcircuitry 70. For the sake of conciseness and clarity, only one of thetwo receive paths is described and illustrated in detail.Analog-to-digital (A/D) converter and down-conversion circuitry 72digitizes and downconverts the analog signal for digital processing. Theresultant digitized signal may be used by automatic gain controlcircuitry (AGC) 74 to control the gain of the amplifiers in the RFcircuitry 70 based on the received signal level.

Preferably, each transmitted frame has a defined structure having twoidentical headers. Framing acquisition is based on the repetition ofthese identical headers. Initially, the digitized signal is provided tosynchronization logic 76, which includes coarse synchronization logic78, which buffers several OFDM symbols and calculates anauto-correlation between the two successive OFDM symbols. A resultanttime index corresponding to the maximum of the correlation resultdetermines a fine synchronization search window, which is used by thefine synchronization logic 80 to determine a precise framing startingposition based on the headers. The output of the fine synchronizationlogic 80 facilitates frame acquisition by the frame alignment logic 84.Proper framing alignment is important so that subsequent FFT processingprovides an accurate conversion from the time to the frequency domain.The fine synchronization algorithm is based on the correlation betweenthe received pilot signals carried by the headers and a local copy ofthe known pilot data. Once frame alignment acquisition occurs, theprefix of the OFDM symbol is removed with prefix removal logic 86 and aresultant samples are sent to frequency offset and Doppler correctionlogic 88, which compensates for the system frequency offset caused bythe unmatched local oscillators in the transmitter and the receiver andDoppler effects imposed on the transmitted signals. Preferably, thesynchronization logic 76 includes frequency offset, Doppler, and clockestimation logic 82, which is based on the headers to help estimate sucheffects on the transmitted signal and provide those estimations to thecorrection logic 88 to properly process OFDM symbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using the FFT processing logic 90.The results are frequency domain symbols, which are sent to processinglogic 92. The processing logic 92 extracts the scattered pilot signalusing scattered pilot extraction logic 94, determines a channel estimatebased on the extracted pilot signal using channel estimation logic 96,and provides channel responses for all sub-carriers using channelreconstruction logic 98. The frequency domain symbols and channelreconstruction information for each receive path are provided to an STCdecoder 100, which provides STC decoding on both received paths torecover the transmitted symbols. The channel reconstruction informationprovides the STC decoder 100 sufficient information to process therespective frequency domain symbols to remove the effects of thetransmission channel.

The recovered symbols are placed back in order using the symbolde-interleaver logic 102, which corresponds to the symbol interleaverlogic 58 of the transmitter. The de-interleaved symbols are thendemodulated or de-mapped to a corresponding bitstream using de-mappinglogic 104. The bits are then de-interleaved using bit de-interleaverlogic 106, which corresponds to the bit interleaver logic 54 of thetransmitter architecture. The de-interleaved bits are then processed byrate de-matching logic 108 and presented to channel decoder logic 110 torecover the initially scrambled data and the CRC checksum. Accordingly,CRC logic 112 removes the CRC checksum, checks the scrambled data intraditional fashion, and provides it to the de-scrambling logic 114 forde-scrambling using the known base station de-scrambling code to recoverthe originally transmitted data.

While certain embodiments are discussed in the context of wirelessnetworks operating in accordance with the IEEE 802.16 broadband wirelessstandard, which is hereby incorporated by reference, the invention isnot limited in this regard and may be applicable to other broadbandnetworks including those operating in accordance with other OFDM-basedsystems including the 3rd Generation Partnership Project (“3GPP”) and3GPP2 evolutions. Similarly, the present invention is not limited solelyto OFDM-based systems and can be implemented in accordance with othersystem technologies, such as code division multiple access technologiesor other frequency division multiple access technologies.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present invention. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

1. A relay station to be associated with a base station and a memberrelay station comprising: transmit and receive circuitry adapted tofacilitate wireless communications with the base station and a mobilestation; and a control system associated with the transmit and receivecircuitry and adapted to: identify a first ranging region within anoverall ranging region to use for a first ranging function, wherein themember relay station uses a second ranging region within the overallranging region for the ranging function; and detect a first ranging codetransmitted by the mobile station via first ranging resources within thefirst ranging region; and process the first ranging code to facilitatethe first ranging function.
 2. The relay station of claim 1 wherein inresponse to detecting the ranging code, the control system is furtheradapted to: obtain transmission adjustments for the mobile terminal touse when transmitting information to the relay station; and send thetransmission adjustments to the mobile station.
 3. The relay station ofclaim 2 wherein the control system is further adapted to providetransmission adjustment recommendations, which are used to determine thetransmission adjustments for the mobile terminal.
 4. The relay stationof claim 3 wherein to obtain the transmission adjustments, the controlsystem is further adapted to: determine transmission adjustmentrecommendations; send code information including or identifying thefirst ranging code and the transmission adjustment recommendations tothe base station; and receive the transmission adjustments from the basestation.
 5. The relay station of claim 4 wherein the control system isfurther adapted to send a mobile station identifier and informationidentifying the first ranging resources or the first ranging regionalong with the code information and the transmission adjustmentrecommendations to the base station.
 6. The relay station of claim 3wherein the control system determines the transmission adjustments basedon the transmission adjustment recommendations.
 7. The relay station ofclaim 3 wherein the transmission adjustment recommendations bear on oneof a group consisting of transmission time, transmission frequency, andtransmission power associated with transmission of the first rangingcode.
 8. The relay station of claim 1 wherein the base station uses athird ranging region within the overall ranging region for the firstranging function.
 9. The relay station of claim 1 wherein the first andsecond ranging regions have common ranging codes, including the firstranging code, that can be assigned to the mobile station.
 10. The relaystation of claim 1 wherein the different ranging codes are provided foreach of the first and second ranging regions.
 11. The relay station ofclaim 1 wherein the wireless communications with the mobile station areprovided using orthogonal frequency division multiplexing, the firstranging region comprises a first group of sub-carriers within a transmitframe, and the second ranging region comprises a second group ofsub-carriers within the transmit frame.
 12. The relay station of claim 1wherein ranging resources of the first ranging region are orthogonal toranging resources of the second ranging region.
 13. The relay station ofclaim 1 wherein the ranging function is an initial ranging functionprovided prior to the mobile station initiating data or voicecommunications via the relay station.
 14. The relay station of claim 1wherein the ranging function is a periodic ranging function providedwhile the mobile station is engaged in data or voice communications viathe relay station.
 15. The relay station of claim 1 wherein the rangingfunction is a handoff ranging function provided while the mobile stationis engaged in a handoff procedure to transition from the relay stationto the member relay station.
 16. The relay station of claim 1 whereinthe ranging function is a handoff ranging function provided while themobile station is engaged in requesting additional bandwidth from therelay station.
 17. The relay station of claim 1 wherein the controlsystem is further adapted to ignore ranging codes transmitted by themobile station via ranging resources of the second ranging region forthe ranging function.
 18. The relay station of claim 1 wherein thecontrol system is further adapted to ignore ranging codes transmitted bythe mobile station via ranging resources outside of the first rangingregion for the first ranging function.
 19. The relay station of claim 1wherein to identify the first ranging region, the control system isadapted to receive a message from the base station, which allocates thefirst ranging region to the first relay station and the second rangingregion to the second relay station.
 20. A base station to be associatedwith a plurality of relay stations capable of facilitating wirelesscommunications with a mobile station, the base station comprising:transmit and receive circuitry adapted to facilitate wirelesscommunications with the plurality of relay stations and the mobilestation; and a control system associated with the transmit and receivecircuitry and adapted to: for each relay station of the plurality ofrelay stations, identify a unique ranging region within an overallranging region to use for a first ranging function; receive a code grabmessage from a first relay station of the plurality of relay stations,the code grab message comprising transmission adjustment recommendationsand a first ranging code or an identifier of the first ranging code thatwas received by the first relay station and transmitted by the mobilestation via first ranging resources within a first ranging region of aplurality of ranging regions; and process the first ranging code tofacilitate the first ranging function.
 21. The base station of claim 20further comprising sending a message to each of the plurality of relaystations to allocate the unique ranging region for each of the pluralityof relay stations.
 22. The base station of claim 20 wherein to processthe first ranging code, the control system is further adapted to:determine transmission adjustments for the mobile station to use whentransmitting information to the first relay station; and send thetransmission adjustments to the first relay station for delivery to themobile station.
 23. The base station of claim 22 wherein the controlsystem is further adapted to: detect a second ranging code transmittedby the mobile station via second ranging resources within a base stationranging region; in response to detecting the second ranging code,determine transmission adjustments for the mobile terminal to use whentransmitting information to the relay station; and send the transmissionadjustments to the mobile station.
 24. The base station of claim 20wherein the code grab message further comprises a mobile stationidentifier and information identifying the first ranging resources orthe first ranging region.
 25. The base station of claim 20 wherein thecontrol system is further adapted to identify for the base station aunique base station ranging region within an overall ranging region touse for the first ranging function, such that each of the plurality ofrelay stations and the base station are allocated different rangingregions for the ranging function.
 26. The base station of claim 25wherein the control system is further adapted to ignore ranging codestransmitted by the mobile station via ranging resources outside of theunique base station ranging region allocated for the base station. 27.The base station of claim 20 wherein the transmission adjustmentrecommendations bear on one of a group consisting of transmission time,transmission frequency, and transmission power associated withtransmission of the first ranging code.
 28. The base station of claim 20wherein ranging resources of each of the plurality of ranging regionsare orthogonal to one another.
 29. The base station of claim 20 whereinthe ranging function is an initial ranging function provided prior tothe mobile station initiating data or voice communications via one ofthe plurality of relay stations.
 30. The base station of claim 20wherein the ranging function is a periodic ranging function providedwhile the mobile station is engaged in data or voice communications viathe relay station.
 31. The base station of claim 20 wherein the rangingfunction is a handoff ranging function provided while the mobile stationis engaged in a handoff procedure to transition from one of theplurality of relay stations to another of the plurality of relaystations.
 32. The base station of claim 20 wherein the ranging functionis a handoff ranging function provided while the mobile station isengaged in requesting additional bandwidth from one of the plurality ofrelay stations.
 33. The base station of claim 20 wherein each of theplurality of ranging regions have common ranging codes that can beassigned to the mobile station.
 34. The base station of claim 20 whereinthe wireless communications with the mobile station are provided usingorthogonal frequency division multiplexing, and each of the plurality ofranging regions comprise unique groups of sub-carriers within a transmitframe.